I don't know how long it takes to install just windows. From the time I installed boot camp to finish installing windows it was around 2 hours. I was leaving the room a lot though to let stuff finish and I didn't always come back to it right when it finished... Of course if you have other stuff to install on top of windows it will get longer.

Time to get a working install with all the patches up to date + virus scanner ? - a lot longer. I personally don't consider an xp installation useful till it's been windows updated'd to the hilt and the virus scanner definitions are up to date.

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